The present invention relates to an actuator device for a control valve and, more particularly, to a piezoelectric actuator device of the type referred to in the preamble to claim 1.
The solution of operating a control valve, for example, a fuel-injection control valve, by means of piezoelectric actuators is known. These devices utilize the mechanical deformation of a piezoelectric element, and preferably of a more complex member such as a bar formed by a series of such elements, for bringing about the operation of a valve-closure member.
Conventionally, the mechanical deformation of the piezoelectric bar consists of a xe2x80x9cpositivexe2x80x9d change in its length along its longitudinal axis, that is, of an elongation of the bar relative to its rest dimension (in order not otherwise to cause mechanical detachment of the elements xe2x80x9cin seriesxe2x80x9d). This elongation leads to linear translation of a free end of the bar, which end is connected to the closure member, relative to the fixed valve body on which the opposite end of the bar is restrained, and consequently causes the closure member to travel between an open position and a closure position, relative to the valve seat.
The mechanical deformation due to the piezoelectric effect is normally very small, of the order of a few tens of microns, and is thus comparable to the dimensional variations produced by the range of temperature variation which is established during the operation of the devices with which the control valve is associated, and to their manufacturing tolerances.
A further problem is that of ensuring efficient operation of the actuator upon the occurrence of long-term intrinsic drift, due particularly to the mechanical components associated with the actuator, for example, owing to wear of the valve seat and the closure member, which is also of a magnitude comparable to the deformations due to the piezoelectric effect.
The aim of the invention is to provide a piezoelectric actuator for a control valve which does not have the disadvantages of the devices of the prior art but which enables the travel of the valve closure member to be controlled effectively, irrespective of the manufacturing tolerances involved and/or of spurious dimensional alterations of the piezoelectric actuating member which may occur during the operation of the device.
According to the present invention, this aim is achieved by means of an actuator having the characteristics recited in claim 1.
In summary, the present invention is based on the principle of restraining one end of the piezoelectric actuating member adjustably on the fixed reference body of the valve relative to which the mechanical deformations of the member are defined, and hence with the ability to compensate for the initial tolerances and for all of the possible spurious dimensional variations which may occur (thermal deformations, long-term dimensional alterations).
In other words, the coupling between the piezoelectric actuating member and the fixed reference body of the valve is formed in a manner such as to be variable and adjustable in operation, so that the system can be said to be self-compensating.
The adjustable connection can be achieved by electromagnetic, piezoelectric, or hydraulic means, either directly or by means of an intermediate member, as will be described in detail below with reference to the currently-preferred embodiments.
The invention provides for an electronic system for adjusting the connection between the piezoelectric actuating member and the fixed reference body to be integrated with the electronic control system of the actuator device, directly in the valve body; temperature control (basically cooling) thereof may be achieved by means of the fluid controlled by the valve, in accordance with a known solution.